Direct access storage devices (DASD) have become part of every day life, and as such, expectations and demands continually increase for greater speed for manipulating data and for holding larger amounts of data. To meet these demands for increased performance, the mechanical assembly in a DASD device, specifically the Head Disk Assembly (HDA) has undergone many changes.
Shown in FIG. 1A is the relationship of components and sub-assemblies of HDA 110 and a representation of data tracks 136 recorded on disk surface 135. The cover is removed and not shown so that the inside of HDA 110 is visible. The components are assembled into base casting 113, which provides attachment and registration points for components and sub-assemblies. Data is recorded onto disk surface 135 in a pattern of concentric rings known as data tracks 136. Disk surface 135 is spun at high speed by means of a motor-hub assembly 130. Data tracks 136 are recorded onto disk surface 135 by means of magnetic head 156, which typically resides at the end of slider 155. FIG. 1A being a plan view shows only one head and one disk surface combination. One skilled in the art understands that what is described for one head-disk combination applies to multiple head-disk combinations. The embodied invention is independent of number of head-disk combinations. Slider 155 and consequently head 156 are incorporated into head gimbal assembly (HGA) 150. HGA 150 is incorporated into actuator 140, which is comprised of at least one arm 146, pivot bearing 145, and voice coil 143. Arm 146 supports HGA 150 over disk surface 135. Pivot bearing 145 allows for smooth and precise rotation of actuator 140. Actuator 140 precisely moves HGA 150 over disk surface 135 by means of electro-motive force (emf) produced between voice coil 143 and magnets 125. Emf is a force that is produced when a current is passed through voice coil 143 and is in close proximity to magnets 125. Only bottom magnet 125 is shown. Top and bottom magnets 125 are joined as pole piece assembly 120. Pole piece assembly 120 in conjunction with voice coil 143 constitutes a voice coil motor (VCM). The VCM positions head 156 via actuator 140 by producing a controlled emf. Current is passed through voice coil 143 from controller 117. The required amount of current from controller 117, to produce the desired amount of emf, is determined by location information (stored in other electronic components not shown in FIG. 1A) for data tracks 136 and location information stored in data tracks 136. Electronic commands for accessing data tracks 136 pass from controller 117 through flex cable 118 and into voice coil 143. Small corrections to the position of head 156 are determined from retrieved information from data tracks 136. This retrieved information is sent back to controller 117 so that small corrections can be made to the location and the appropriate current can be sent from controller 117 to voice coil 143. Once the desired data track is located, data is either retrieved or manipulated by means of electronic signals that pass through connector 111 and through flex cable 118. Connector 111 is the electronic interface that allows data to be transferred in and out of HDA 110.
The dynamic performance of HDA 110 is a major mechanical factor for achieving higher data capacity as well as for manipulating this data faster. The dynamic performance of HDA 110 is dependent upon the dynamic performance of its individual components and sub-assemblies. Many factors that influence the dynamic performance are intrinsic to the individual components. Some of these intrinsic factors are in general: mass of the component; stiffness of the component; and geometry of the component. This is not an all-inclusive list and those schooled in engineering or HDA technology will understand that there are many other factors that influence dynamic performance of HDA 110 components and sub-assemblies.
The quantity of data tracks 136 recorded on disk surface 135 is determined partly by how well magnetic head 156 can be positioned and made stable over a desired data track 136. The quantity of data track 136 is a direct indicator of the amount of data stored. Although the mass, stiffness and geometry of the components in actuator 140 directly affect the stable positioning of magnetic head 156, vibration energy that acts on actuator 140 and its components is also a major factor in the stable positioning of head 156. If excessive, vibration energy will impart oscillating motion to actuator 140 and move head 156 from a desired position over data track 136.
There are several sources for vibration energy that act on actuator 140. There is outside vibration energy that enters HDA 110 through base casting 113 and affects the stability of actuator 140. There is internal vibration energy that is produced by rotating components and sub-assemblies inside HDA 110. Motor-hub assembly 130 can transmit vibration energy through base casting 113 and into actuator 140. Spinning disk surface 135 can impart oscillating motion directly into magnetic head 156 and cause it to move off data track 136. And pivot bearing 145 can also transmit vibration energy into actuator 140 and thus into magnetic head 156. Attention is given to all potential sources of vibration energy in the design of these sub-assemblies and components. Another source of vibration energy inside HDA 110 is the motion of the atmosphere inside HDA 110 and its interaction with sub-assemblies and components.
Shown in FIG. 1B is the relationship of components and sub-assemblies during assembly of HDA 110 as described by FIG. 1A. Included in FIG. 1B are cover 115 and both magnets 125.
It has been recognized by HDA designers that it is desirable to control the atmosphere inside the HDA. The atmosphere can be controlled for its humidity as cited in U.S. Pat. No. 6,762,909 or the atmosphere can be controlled for its gas composition. In light of the aforementioned problem of atmosphere inside the HDA impacting HDA components and imparting vibration energy, it has been recognized that a low-density gas, such as helium (He), has the benefit of imparting less energy into HDA components. It is well known that the aerodynamic forces on an object are proportional to the product of the density and square of the velocity of the impinging fluid. By virtue of the lower density of He, it will impart smaller lift and drag forces into HDA components as the internal gas of the HDA impinges on the internal components of the HDA.
Once a desired atmosphere or mixture of gases is introduced inside an HDA, it must be contained or maintained. US Patent Application 2003/0081349 teaches how to replenish the mixture of gases from a reservoir and valve system if the mixture of gases cannot be contained. Emphasis has been placed on containing a mixture of gases once it has been established. The general term for containing and sealing in a gas or atmosphere is a hermetic seal. Partial containment is a semi-hermetic seal. Hermetic seals have taken several forms. Much attention has been given to sealing HDAs by various means of welding. In general, welding is the assembly technique by which two parts to be joined are held together, their mating surfaces heated above their melting temperatures either by applying molten material of similar composition or applying heat directly to the mating surfaces. U.S. Pat. No. 6,762,909 cites welding as a method to achieve a hermetic seal. The high temperatures required for welding has made this approach difficult to apply to the hermetic sealing of an HDA. Other approaches for making a welded hermetic seal are taught in US Patent Application 2003/0223148 and Japanese Patent JP8161881. 2003/0223148 cites laser welding as a means to achieve a welded hermetic seal. Japanese Patent JP8161881 teaches the use of a welded metallic ribbon.
Hermetic seals have also been described that use the folding, or hemming of metal in conjunction with a compliant sealing material. Hemming is the process by which thin sheets are placed together so they overlap at an edge and are secured to each other by folding the overlapping edges together. Both U.S. Pat. Nos. 4,367,503 and 6,556,372 teach variations for hemming metal with a compliant material in the hem.
Secondary enclosures and covers have also been described in the art. US Patent Application 2003/0179489 teaches the use of a structural cover that provides a semi-hermetic seal, followed by a sealing cover that attaches to the base casting and on top of the structural cover that provides the hermetic seal. Japanese Patent JP5062446 teaches placing a generally conventional HDA inside a hermetically sealed outer container.
The challenges to the above cited art include but are not limited to: distortion of HDA components and sub-assemblies due to the high temperature required for welding; restriction of the choice of materials for the base and cover so as to be suitable for welding; the use of multiple components for isolating HDA components and sub-assemblies from welding temperatures; rework procedures that might be required due to failed HDA components or sub-assemblies.